Enzyme Induction and Repression — MCQs
A factor that is likely to increase the duration of action of a drug that is partially metabolized by CYP3A4 in the liver is:
Which of the following is considered a fundamental defense mechanism in psychology?
Which drug is suitable for epilepsy related to a brain tumor?
Which bacterium is particularly notorious for producing extended-spectrum beta-lactamases (ESBLs) and carbapenemases, contributing to significant antibiotic resistance in hospital settings?
Which of the following is active in dephosphorylated state?
Production of inactivating enzymes is an important mechanism of drug resistance for all of these antibiotics EXCEPT
Which of the following does NOT directly influence the activity of existing enzyme molecules?
Which kinetic parameter is primarily associated with enzyme specificity?
Enzyme causing covalent bond cleavage without hydrolysis ?
Acetyl CoA carboxylase is stimulated by all except which of the following?
Enzyme Induction and Repression Indian Medical PG Practice Questions and MCQs
Question 1: A factor that is likely to increase the duration of action of a drug that is partially metabolized by CYP3A4 in the liver is:
- A. Chronic administration of phenobarbital with the drug
- B. Displacement from tissue binding sites by another drug
- C. Chronic administration of rifampicin
- D. Chronic administration of cimetidine with the drug (Correct Answer)
Explanation: ***Chronic administration of cimetidine with the drug*** - **Cimetidine** is a potent inhibitor of various **cytochrome P450 (CYP450) enzymes**, including **CYP3A4**. - By inhibiting the metabolism of a drug predominantly metabolized by **CYP3A4**, cimetidine will increase its plasma concentration and extend its **duration of action**. *Chronic administration of phenobarbital with the drug* - **Phenobarbital** is a strong **inducer of CYP450 enzymes**, including **CYP3A4**. - Induction would accelerate the metabolism of the drug, thus **decreasing its duration of action**, not increasing it. *Displacement from tissue binding sites by another drug* - Displacement from tissue binding sites would primarily increase the **free fraction of the drug in the plasma**, leading to a more rapid distribution to eliminating organs and potentially **shorter duration of action** if elimination is extraction-limited. - This mechanism does not directly impact the **metabolic rate** unless clearance is significantly altered through increased availability for metabolism. *Chronic administration of rifampicin* - **Rifampicin** is a potent **inducer of CYP3A4** and other CYP enzymes. - Its administration would lead to **increased metabolism** of the co-administered drug, thereby **reducing its duration of action**.
Question 2: Which of the following is considered a fundamental defense mechanism in psychology?
- A. Alienation
- B. Confabulation
- C. Repression (Correct Answer)
- D. Suppression
Explanation: ***Repression*** - **Repression** is the **fundamental unconscious defense mechanism** where unacceptable thoughts, feelings, or memories are pushed out of conscious awareness to protect the ego. - It is considered the foundational defense mechanism because it operates automatically and without conscious effort, forming the basis for many other defense mechanisms. *Alienation* - **Alienation** refers to a feeling of estrangement or disconnection from others, society, or oneself, often due to social or psychological factors, but it is not a defense mechanism. - It describes a state of being rather than an active psychological process used to cope with anxiety. *Confabulation* - **Confabulation** is the creation of false autobiographical memories without the intent to deceive, often seen in neurological conditions like **Korsakoff's syndrome**. - It is a symptom of memory impairment, not an active psychological defense mechanism. *Suppression* - **Suppression** is a defense mechanism but is considered a mature/conscious defense; it involves deliberately and consciously putting unwanted thoughts or feelings out of mind. - Unlike **repression**, **suppression** is an intentional and relatively aware act of avoiding disturbing thoughts.
Question 3: Which drug is suitable for epilepsy related to a brain tumor?
- A. Levetiracetam (Correct Answer)
- B. Phenytoin
- C. Phenobarbitone
- D. Carbamazepine
Explanation: ***Levetiracetam*** - Levetiracetam is often preferred for **tumor-related epilepsy** due to its favorable **pharmacokinetic profile**, minimal **drug-drug interactions**, and broad spectrum of activity against various seizure types. - It does not significantly induce or inhibit hepatic enzymes, making it a safer option for patients who may be on other medications for their tumor or cancer treatment. *Phenytoin* - **Phenytoin** has a narrow **therapeutic window** and significant **drug-drug interactions** due to its potent hepatic enzyme induction, which can complicate concomitant use with **chemotherapy** or other medications. - It also has a dose-dependent non-linear pharmacokinetic profile, making dose adjustments challenging and increasing the risk of **toxicity**. *Phenobarbitone* - **Phenobarbitone** is a potent enzyme inducer and has a high potential for **sedation** and cognitive side effects, which can significantly impair the quality of life for patients. - Its long half-life and propensity for **drug interactions** make it less desirable, especially in patients with brain tumors who may experience other neurological deficits. *Carbamazepine* - **Carbamazepine** is another potent **enzyme inducer** that can lead to significant **drug interactions**, particularly with chemotherapy agents, altering their metabolism and efficacy. - It often causes side effects like **drowsiness**, **dizziness**, and can lead to **hyponatremia**, which may be problematic in patients who are already compromised.
Question 4: Which bacterium is particularly notorious for producing extended-spectrum beta-lactamases (ESBLs) and carbapenemases, contributing to significant antibiotic resistance in hospital settings?
- A. Pseudomonas
- B. Staphylococcus
- C. Streptococcus
- D. Klebsiella (Correct Answer)
Explanation: ***Klebsiella*** - **_Klebsiella pneumoniae_** is particularly well-known for producing a wide range of beta-lactamases, including both **Extended-Spectrum Beta-Lactamases (ESBLs)** and **carbapenemases**, making it a significant cause of **hospital-acquired infections** that are difficult to treat. - The presence of these enzymes allows it to hydrolyze and inactivate many commonly used antibiotics, leading to **multidrug resistance**. *Pseudomonas* - While *Pseudomonas aeruginosa* can produce various resistance mechanisms, including **carbapenemases (e.g., VIM, IMP)** and **AmpC beta-lactamases**, it is not as frequently associated with ESBL production as *Klebsiella*. - *Pseudomonas* is notorious for its intrinsic resistance to many antibiotics and its ability to form **biofilms**. *Staphylococcus* - **_Staphylococcus aureus_** is well-known for **Methicillin-Resistant *Staphylococcus aureus* (MRSA)**, which is resistant to beta-lactam antibiotics due to the acquisition of the **_mecA_ gene**, encoding altered penicillin-binding proteins. - However, *Staphylococcus* species are not commonly associated with the production of ESBLs or carbapenemases in the same way Gram-negative bacteria like *Klebsiella* are. *Streptococcus* - While some streptococcal species can develop resistance to antibiotics like **penicillin and macrolides**, they are not typically associated with the production of ESBLs or carbapenemases. - Resistance in *Streptococcus pneumoniae*, for example, often involves **alterations in penicillin-binding proteins**, similar to MRSA.
Question 5: Which of the following is active in dephosphorylated state?
- A. PEPCK
- B. Pyruvate Carboxylase
- C. Glycogen Synthase (Correct Answer)
- D. Glycogen Phosphorylase
Explanation: ***Glycogen Synthase*** - **Glycogen synthase** is primarily active in its **dephosphorylated state**, which is promoted by insulin and signals glycogen synthesis. - Dephosphorylation relieves the inhibitory effect of phosphorylation, allowing the enzyme to efficiently add glucose units to a **growing glycogen chain**. *PEPCK* - **Phosphoenolpyruvate carboxykinase (PEPCK)** activity is primarily regulated at the transcriptional level, not typically by phosphorylation state for activation. - Its expression is induced by **glucagon** and **cortisol** during gluconeogenesis. *Pyruvate Carboxylase* - **Pyruvate carboxylase** is allosterically activated by **acetyl-CoA** and its activity is not directly regulated by phosphorylation/dephosphorylation in the same manner as glycogen synthase. - This enzyme plays a key role in **gluconeogenesis** by converting pyruvate to oxaloacetate. *Glycogen Phosphorylase* - **Glycogen phosphorylase** is active in its **phosphorylated state**, particularly the 'a' form, which is promoted by glucagon and adrenaline for glycogen breakdown. - Phosphorylation activates the enzyme, leading to the **breakdown of glycogen** into glucose-1-phosphate.
Question 6: Production of inactivating enzymes is an important mechanism of drug resistance for all of these antibiotics EXCEPT
- A. Quinolone (Correct Answer)
- B. Penicillin
- C. Chloramphenicol
- D. Aminoglycoside
Explanation: ***Quinolone*** - The primary mechanisms of resistance to **quinolones** involve mutations in the **gyrase** and **topoisomerase IV** enzymes or efflux pump overexpression, rather than enzymatic inactivation of the drug itself. - Unlike other antibiotic classes listed, quinolones are not typically susceptible to bacterial enzymes that degrade or modify their structure. *Penicillin* - **Penicillins** are highly susceptible to inactivation by **beta-lactamase enzymes**, which hydrolyze the beta-lactam ring, rendering the antibiotic ineffective. - This enzymatic degradation is a major mechanism of resistance developed by many bacterial species to penicillin and other beta-lactam antibiotics. *Chloramphenicol* - Resistance to **chloramphenicol** is primarily mediated by the enzyme **chloramphenicol acetyltransferase (CAT)**, which acetylates the drug, preventing its binding to the bacterial ribosome. - This enzymatic modification is a classic example of drug inactivation leading to resistance. *Aminoglycoside* - **Aminoglycosides** are frequently inactivated by a variety of **aminoglycoside-modifying enzymes (AMEs)**, such as acetyltransferases, phosphoryltransferases, and nucleotidyltransferases. - These enzymes add chemical moieties to the aminoglycoside molecule, preventing its binding to the bacterial ribosome and inhibiting protein synthesis.
Question 7: Which of the following does NOT directly influence the activity of existing enzyme molecules?
- A. Acetylation
- B. Phosphorylation
- C. Induction (Correct Answer)
- D. Methylation
Explanation: ***Induction does NOT directly influence existing enzyme activity.*** - **Enzyme induction** refers to the process where the **synthesis rate** of an enzyme is increased, typically in response to specific substrates or substances. - This leads to a **higher concentration** of the enzyme, rather than directly modifying the catalytic activity of existing enzyme molecules. - Induction increases **enzyme quantity**, not the activity of pre-existing enzymes. *Incorrect: Acetylation directly influences enzyme activity.* - **Acetylation** is a reversible post-translational modification that involves the addition of an **acetyl group** (CH3CO) to existing enzyme molecules, typically at lysine residues. - This modification can alter the enzyme's **conformation**, substrate binding, and catalytic efficiency, thereby directly influencing its activity. *Incorrect: Phosphorylation directly influences enzyme activity.* - **Phosphorylation** is one of the most important regulatory mechanisms where a **phosphate group** is added to existing enzyme molecules, often by kinases. - This modification can **activate or inactivate** enzymes by changing their shape or charge, thus directly altering their catalytic activity. - Classic examples: glycogen phosphorylase, hormone-sensitive lipase. *Incorrect: Methylation directly influences enzyme activity.* - **Methylation** involves the addition of a **methyl group** to existing enzyme molecules, commonly at lysine or arginine residues. - This post-translational modification can directly impact enzyme function by altering conformation and substrate binding.
Question 8: Which kinetic parameter is primarily associated with enzyme specificity?
- A. Both
- B. Km
- C. Vmax
- D. None of the options (Correct Answer)
Explanation: ***None of the options*** - **Enzyme specificity** is primarily determined by the unique three-dimensional **active site structure** of the enzyme, which allows it to bind only to specific substrates through complementary shape and chemical interactions. - This structural complementarity involves steric fit and specific non-covalent interactions (hydrogen bonds, van der Waals forces, electrostatic interactions) between the enzyme and its substrate. - **Neither Km nor Vmax are determinants of enzyme specificity**—they are kinetic parameters that describe enzyme behavior, not structural selectivity. *Km (Michaelis constant)* - Represents the substrate concentration at which the reaction rate is half of Vmax. - Indicates the **affinity** of an enzyme for its substrate (lower Km = higher affinity). - While enzymes may show different Km values for different substrates, **Km reflects binding affinity, not the structural basis of specificity**. *Vmax (Maximum velocity)* - The maximum rate of reaction when the enzyme is saturated with substrate. - Reflects **catalytic efficiency** and the amount of active enzyme present. - Does not relate to the enzyme's ability to discriminate between different substrate molecules. *Both* - Incorrect because neither Km nor Vmax determines which substrates an enzyme can recognize and bind. - Enzyme specificity is a **structural property** of the active site, while Km and Vmax are **kinetic properties** that describe reaction rates.
Question 9: Enzyme causing covalent bond cleavage without hydrolysis ?
- A. Lyase (Correct Answer)
- B. Ligase
- C. Hydrolase
- D. Transferase
Explanation: ***Lyase*** - **Lyases** are enzymes that catalyze the cleavage of **covalent bonds** (C-C, C-O, C-N, and others) by means other than hydrolysis or oxidation, often creating a new double bond or a ring structure. - They remove groups from substrates to form double bonds, or conversely, add groups to double bonds. - **Examples:** Aldolase (cleaves C-C bonds in glycolysis), carbonic anhydrase (reversible cleavage of C-O bond), fumarase (C-C bond cleavage in TCA cycle). *Ligase* - **Ligases** are enzymes that join two large molecules by forming a new chemical bond, usually accompanied by the **hydrolysis of ATP**. - They are involved in synthesis reactions, not the cleavage of bonds. *Hydrolase* - **Hydrolases** specifically catalyze the hydrolysis of a chemical bond, involving the **addition of water** across the bond. - They break down large molecules into smaller ones using water - this is the key difference from lyases. *Transferase* - **Transferases** catalyze the transfer of a **functional group** from one molecule (the donor) to another (the acceptor). - They do not cause covalent bond cleavage without hydrolysis but rather move existing groups between molecules.
Question 10: Acetyl CoA carboxylase is stimulated by all except which of the following?
- A. Acyl CoA (Correct Answer)
- B. ATP
- C. Insulin
- D. Citrate
Explanation: ***Acyl CoA*** - **Acyl CoA** (specifically long-chain fatty acyl CoAs) is an **inhibitor** of acetyl CoA carboxylase (ACC), signifying an abundance of fatty acids and a need to reduce further synthesis. - This feedback inhibition helps regulate **fatty acid synthesis**, ensuring that the pathway is downregulated when sufficient fatty acids are present. *Citrate* - **Citrate** is a potent **allosteric activator** of acetyl CoA carboxylase, indicating a high energy state and excess mitochondrial acetyl CoA, which can be channeled into fatty acid synthesis. - Its presence promotes the polymerization of ACC monomers into active polymers, enhancing enzyme activity. *ATP* - **ATP** is required as a substrate for the carboxylation reaction catalyzed by ACC, providing the energy for the formation of **malonyl CoA**. - High levels of ATP indirectly signal a state of energy abundance, which favors anabolic processes like fatty acid synthesis. *Insulin* - **Insulin** is a hormonal activator of acetyl CoA carboxylase, promoting its dephosphorylation via **protein phosphatase 2A**. - This dephosphorylation leads to increased enzyme activity, stimulating **fatty acid synthesis** in response to high blood glucose after a meal.
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